Attorney's fees or attorneys' fees are the costs of legal representation that an attorney's client or a party to a lawsuit incurs. Attorney's fees are assessed in a number of ways, usually set by contract in advance of the representation, including by billable hours, flat fees, or contingent fees. Attorneys who voluntarily accept work on behalf of indigent clients often work pro bono. An upfront fee paid to a lawyer is called a retainer. Money within the retainer is often used to "buy" a certain amount of work. Some contracts provide that when the money from the retainer is gone, the fee is renegotiated.